相对密度the mass of a substance divided by the mass of the same volume of water or air
un.
1.
相对密度
2.
比重
n.
1.
theratioofthedensityofasubstancetothedensityofastandardsubstanceatthesametemperatureandpressure. Forliquidsandsolidsthestandardsubstanceisusuallywater, forgases, air.